The present invention is directed to space heating furnaces, and is in particular directed to an induction furnace of the type in which outside combustion air is supplied through a combustion air duct to the burners of the furnace and in which an inducer fan or blower exhausts the combustion products out through a vent duct.
The invention is more specifically directed to a furnace that can be installed in an conventional upflow configuration, an inverted, downflow configuration, or in a horizontal, i.e., right flow or left flow configuration, requiring only a nominal reconfiguration of the internal parts of the furnace.
Induction type furnaces have gained popularity in recent times because of their high efficiency and because they do not require a conventional stack for exhaust.
In a furnace of this type an inducer blower is energized to induce a draft, i.e. a flow of combustion air through the furnace heat exchanger. Combustion air is furnished from the outside environment through a combustion air duct or pipe to the furnace where it is coupled to an air inlet shoe. This air inlet shoe opens to a burner box that contains the gas burners. The latter are ignited when the inducer operates, and hot combustion products are fed into the heat exchanger. The heat exchanger is typically a two-stage system, with a primary heat exchanger stage, so called because most of the heat from the combustion gases is transferred to the circulating air from this heat exchanger. The primary heat exchanger is then followed by a secondary or condensing heat exchanger so called because water vapor in the combustion gases condenses here to yield additional heat. The inducer fan is then connected at the condensing heat exchanger's outlet and sends the exhaust through the vent pipe into the outside environment.
A furnace blower moves circulating room air from a return air duct, coupled to a comfort space, across the furnace heat exchanger to pick up heat. The heated circulation air then goes into a hot air plenum and is distributed through hot air ductwork back to the comfort space.
Under certain outdoor conditions, condensation can occur in the combustion air duct and must be drained out from the system. To drain accomplish condensate from the combustion air intake shoe, a drain line is attached to it, which leads down to a sump or trap device.
The air intake shoe is disposed on the wall of the burner box that is beneath the box when the furnace is poised in the conventional or upflow orientation. The combustion air pipe enters the furnace cabinet horizontally, i.e., through a side wall, to connect to the air intake shoe.
In the upflow orientation, drainage is not a difficult problem, as the condensate collects in the lower part of the shoe and then enters a drain line disposed at the lower part of the shoe.
In a horizontal orientation of the furnace, the combustion air pipe and the air inlet shoe are disposed vertically, so any condensate will collect at the lower side of the shoe, i.e., away from the combustion air pipe, and can be drained away easily.
However, it is in the inverted or downflow orientation of the furnace that drainage becomes a problem. Here, the air inlet shoe is oriented above the associated burner box, where the condensate can drip into the burner box causing corrosion. Accordingly, the air inlet shoe has to be suitably designed to address the problem of condensation in the downflow orientation, without significantly impairing combustion air intake, and further permitting the furnace to be installed in its other orientations.